1. Field of the Invention
The invention concerns a supporting floor for the core of a nuclear reactor. More particularly, the supporting floor comprises a plurality of graphite blocks arranged in vertical columns. The nuclear reactor, preferably a gas cooled nuclear reactor, comprises a reactor core in the form of a pile of spherical fuel elements surrounded by a cylindrical side reflector and a thermal side shield arranged at a distance from the side reflector. The vertical columns of the supporting floor are provided with bores in the longitudinal direction and rest on the base of the nuclear reactor itself.
2. Background of the Prior Art
West German Offenlegungsschrift No. 1 956 226 discloses a gas cooled nuclear reactor having a core of graphite blocks arranged in vertical columns. The core is supported on the floor of the reactor pressure vessel by means of several layers of a refractory material, for example, graphite. Each column of the core is supported by its own supporting column. The supporting columns consist of several graphite blocks stacked on top of each other. Access for the cooling gas to the core is provided by means of channels formed into the graphite blocks of the support layers and connected with gas conduits in the core and with a gas space outside the core. The entire structure of supporting columns is surrounded by packing blocks arranged between the structure and the lining of the pressure vessel.
West German Published Application No. 1 261 606 shows a nuclear reactor with a radiation reflector inserted between the thermal shield and the core of the reactor. The reflector consists of a lateral reflector enclosing a cylindrical cavity and a lower reflector serving as the supporting floor. The lower reflector is formed by two layers of ashlar shaped graphite blocks differing in their longitudinal direction from one layer to the other. In each of the layers the blocks arranged around a central opening are maintained together and locked against each other by means of wedges. The lateral reflector, which consists of graphite blocks stacked in layers, one upon the other, is supported by the thermal side shield. A plurality of elastic structural parts acting in the radial direction provides this support.
The prior art further includes a supporting floor for a pebble bed reactor consisting of a gas permeable supporting layer of spheres of high temperature resistant material and a support structure designed for the weight of the supporting pebble bed layer and the fuel elements. The fuel elements are piled directly onto the supporting pebble layer. A layer of high temperature resistant tiles is arranged between the support structure and the supporting pebble layer.
In another pebble bed reactor, the THTR-300 MWe, the support floor for the pile of fuel pellets comprises a plurality of hexagonal graphite blocks arranged in freely movable columns and containing axial bores for the cooling gas. Each column formed by the graphite blocks is supported individually by a circular column. The circular column is built into a floor of graphite plates. The expansion gaps obtained by a reduction of the nominal dimensions of the graphite blocks permit the unimpaired thermal expansion of the elements of the support floor without exceeding the overall dimensions. Under certain non-stationary operating conditions, or in the case of failures, respectively, these gaps may add up and relatively large individual gaps may be formed. However, in view of the dimensions of the THTR-300 MWe, the restoring forces required to close the gaps are of negligible importance.
A supporting structure for a pebble bed reactor of greater capacity is known from West German Offenlegungsschrift No. 27 18 493. This support structure consists of several layers of prismatic graphite blocks arranged over each other and built up as a closed unit without expansion gaps. The blocks of one layer are keyed into the blocks of the adjacent layer. The preferred hexagonal graphite blocks display widths across their flats in the upper layers that are different from those in the bottom layer, which is formed of a plurality of supporting units. Each supporting unit is resting in its central area of a circular column and is composed of a number of carrier segments. The support structure represents a stable and rigid plate. Because of the keying of the prismatic blocks, no restoring force is required. However, in the case of this known structure, certain specific measures must be taken to counter the deformations occurring in the bottom layers of the nuclear reactor or in the bottom of the pressure vessel, respectively.